1. Field of the Invention
The present invention relates to document processing machines and particularly to a controller for monitoring and controlling the operation of the track portion of a document handling machine, where the track portion lies between the feeder portion, which receives documents, and the sorter portion, which dispenses documents in ordered groups. It relates more particularly to the detection of conditions incipient to jamming in the track and to steps to minimize the effects of jamming including stopping the delivery of documents from the feeder portion, stopping portions of the track which are directly involved in the jamming area, and stopping the remaining portions of the system after first allowing clearance of documents from all portions not directly involved in the jamming.
2. Description of the Prior Art
Exemplary prior art for preventing jamming in document processing equipment is disclosed in U.S. Pat. No. 4,151,410 to Andrew H. McMillan and William B. Templeton, entitled "Document Processing, Jam Detecting Apparatus and Process" which issued Apr. 24, 1979. Apparatus according to that patent employs sensors spaced along document transport tracks to monitor the passage of the documents. Typically, the sensors are used to detect the translucency of each document. Translucency is variable through a document in motion because of irregularities in the paper. If no changes in translucency are perceived for a time while the equipment is running, it is understood that the document has stopped moving and the equipment has probably jammed. While that patent is believed to concern relevant prior art, the present invention, as claimed, is clearly patentable thereover.
Another example of relevant prior art is to be found in a copending U.S. Pat. application Ser. No. 108,797 filed Dec. 31, 1979 in the name of John M. Chambors and entitled "Jam Detection and Recovery Systems". Now U.S. Pat. No. 4,275,293. That application relates to document sorting systems and particularly relates to apparatus for detecting jamming of documents in document sorting tracks and to the prevention of further jamming. The system involves detecting conditions attendent to jamming in document handling tracks and taking immediate action to prevent the introduction of new documents into a track while clearing the track by routing documents to their proper pocket destinations or to a missort pocket.
Prior art devices such as those outlined above have functioned well in earlier models of document processing equipment, but have not been found to be satisfactory in present machines which operate at higher speeds. In addition, when a jam condition starts to develope, a need exists with present apparatus to clear the machine at a higher speed than formerly, which includes stopping the machine feeder to prevent the entry of further documents into the track and then clearing the track. Clearing the track, as conceived for the present apparatus, involves completing the clearance of documents from the track upstream and downstream of the point at which the jam occurs while providing signals to the sorter portion to enable the latter to continue operating until documents have been cleared from the sorter. These more stringent requirements have led to a search for better means and to the development of the present invention.